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Am Thu, 08 Feb 2018 14:50:31 -0500 schrieb Rich Freeman: |
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> On Thu, Feb 8, 2018 at 2:17 PM, Dale <rdalek1967@×××××.com> wrote: |
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>> As someone else pointed out, if you start using swap, that generally |
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>> defeats the purpose of tmpfs. |
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>> |
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>> |
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> I'll just add one thing to this, which I've probably already said ages |
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> ago: |
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> |
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> In an ideal world swap would STILL be better than building on disk, |
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> because it gives the kernel fewer constraints around what gets written |
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> to disk. |
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> |
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> Anything written to disk MUST end up on the disk within the dirty |
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> writeback time limit. Anything written to tmpfs doesn't ever have to |
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> end up on disk, and if it is swapped the kernel need not do it in any |
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> particular timeframe. Also, the swapfile doesn't need the same kinds of |
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> integrity features as a filesystem, which probably lowers the cost of |
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> writes somewhat (if nothing else after a reboot there is no need to run |
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> tmpreaper on it). |
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> |
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> So, swapping SHOULD still be better than building on disk, because any |
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> object file that doesn't end up being swapped is a saved disk IO, and |
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> the stuff that does get swapped will hopefully get written at a more |
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> opportune time vs forcing the kernel to stop what is doing after 30s (by |
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> default) to make sure that something gets written no matter what (if it |
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> wasn't deleted before then). |
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I can only second this. |
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> That's all in an ideal world. In practice I've never found the kernel |
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> swapping algorithms to be the best in the world, and I've seen a lot of |
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> situations where it hurts. I run without a swapfile for this reason. |
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> It pains me to do it because I can think of a bunch of reasons why this |
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> shouldn't help, and yet for whatever reason it does. |
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I really prefer having inactive things being swapped out than discarding |
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cache from memory. But since kernel 4.9 this no longer works so well. I'm |
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still seeking the reason. But for that reason, building in tmpfs is no |
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longer such an appealing option as before. |
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Otherwise, I was quite happy with swap behavior, exactly for the reasons |
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you initially outlined. |
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-- |
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Regards, |
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Kai |
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Replies to list-only preferred. |
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